Reinforcement in red: Cummins launching new generation Tier 3 QSB engines at ConExpo; new engines, new look belies consistent message on emissions technology

Diesel Progress North American Edition,  March, 2005  by Mike Brezonick

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The new QSB engines incorporate electronically controlled Bosch common rail fuel systems and four-valves-per-cylinder head designs, with the injector vertically centered for more precise injection. The system, which is similar to the system on the Cummins Euro 3 on-highway engines, is capable of multiple injection events--such as pilot and post injection--within a single injection cycle, which can provide improved responsiveness as well as reduced smoke, particularly in cold-start conditions. The common rail system can deliver injection pressures as high as 23,000 psi, but Britt noted that "we're finding we're not having to go anywhere near that, which is an added bonus in terms of reliability and durability."

The injection system is controlled by a CM850 electronic control module built by Motorola. Cummins uses a common electronics architecture with an identical OEM interface for all of its engines from 4.5 L through 15 L, connected through a 50-pin Deutsch connector. "That's really helpful for OEMs that use several of our engines," Britt said.

All of the electronically controlled Tier 3 QSB engines also incorporate Holset wastegated turbochargers. "It's fairly straightforward turbocharger technology." said Tim Meyer, marketing, Cummins Tier 3 applications. "We offer variable geometry products in on-highway, but in this market, we thought we could do well with wastegate turbocharging. It offers very high reliability because we haven't added a lot of sensors, we haven't added a lot additional technology and componentry.

"The approach we took for Tier 3 was to minimize the impact of installation to our OEMs and our customers, so they don't have a large tear-up of the product line. In most instances, we can slide the Tier 3 engine into where the Tier 2 engines had been. Because they utilize the in-cylinder solution, we don't have a lot of extra hardware hanging on the outside."

Along with exhaust emissions, significant improvements have also been made to the QSB engines with an eye toward the other emission noise. Cummins said that noise emissions have been reduced by as much as 5 to 9 db(A), depending on model and configuration, which is more than a 55% reduction in sound pressure. The block incorporates a more sculpted, ladder flame design for improved stiffness and the geartrain has been moved from the front to the rear of the engine, which reduces torsionals and gear chatter. A bolted bed plate has been added to the underside of the block to reduce lower end flexing and the tappet cavities have been enclosed within the block itself. "There used to be a flat plate that bolted over the top of the tappet cavity," Britt said. "We've closed that in as part of the casting.

"The valve cover is isolated, so there is not a drumming action on the top, and the high-pressure common rail fuel system has relatively lower drive torque, but also the pilot injection is just a huge aid in reducing noise.